Subj : Re: sigwait() is not catching SIGUSR1 signal
To   : comp.programming.threads,comp.unix.programmer
From : Roopa
Date : Fri Mar 11 2005 02:17 am


Neelakantan wrote:
> Hi,
>
>      i have a problem with sigwait() in a multithreaded program.
>
>      In this program some thread will be generating the signal
SIGUSR1 at
>      some time(asynchronously) and there is a dedicated thread for
handling
>      the asynchronous(SIGUSR1 in my case) signals.
>
>      The sinal handling thread uses sigwait() to catch the signal,
however
>      the signal is not caught by the sigwait() function. I have
blocked the
>      signal SIGUSR1 before the threads are created aswell before the
sigwait()  is called.
>

       If its not caught then your registered signal handler isnt
registered
       properly with the OS. !

       You need to override the default signal handling by OS with your
       signal handlers at the right place :-)
       May be reading your OS documentation on signal handlers might be
of
       some clue/help of howto accomplish it.

- Roopa

>      I have included a variant of the program.
>
>      Any help will be highly appreciated.
>
>      Thanks and regards,
>
>      Neelakantan
>



> *****************************************************************
>      OS : Redhat 9 kernel version 2.4.20
>
>      Compiler: g++ (GCC) 3.2.2 20030222 (Red Hat Linux 3.2.2-5).
>
>      Note: if i send the signal SIGUSR1 from the command prompt,
>            the signal has been caught.
>
> ****************   sinal.cpp ************************************
> #include<iostream>
> #include<pthread.h>
> #include<signal.h>
> #include<errno.h>
> #include<unistd.h>
> using namespace std;
> void* fun(void* arg)
> {
>         int i = 0;
>         while(i<10)
>         {
>           sleep(2);
>           kill(getpid(),SIGUSR1);
>           cout << "SIGUSR1 Has been sent" << i++ << endl;
>         }
>         return NULL;
> }
> int main()
> {
>         pthread_t tid;
>         sigset_t set;
>         sigemptyset(&set);
>         sigaddset(&set, SIGUSR1);
>         sigaddset(&set, SIGINT);
>         pthread_sigmask(SIG_BLOCK, &set, NULL);
>         int status = pthread_create(&tid,0,fun,0);
>         if (status != 0)
>         {
>           cout << "Thread Creation Failed" << endl;
>           exit(0);
>         }
>         int signal = 0;
>         while(true)
>         {
>           sigwait(&set,&signal);
>           if (signal == SIGUSR1)
>            {
>                 cout << "SIGUSR1 signal recieved" << endl;
>                 break;
>            }
>           if(signal == SIGINT)
>            {
>                 cout << "SIGINT signal recieved" << endl;
>                 break;
>            }
>         }
>         cout << "Main is exiting" << endl;
>         exit(0);
> }
> ******************* signal.cpp ends ***************************

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